This invention generally concerns a structural joint, and more specifically concerns a gusset connection that allows greater relative movement between connected structural members and simplifies erection in the field.
FIG. 1A shows a typical prior art gusset connection in a braced frame structure. A horizontal structural member Bm (beam) is connected to a vertical structural member C (column). To connect the diagonal structural member Br (i.e., brace) to the beam-column assembly, a gusset plate G is used. The brace is connected (e.g., pinned, bolted) to the gusset and the gusset is connected to both the beam and the column, typically by welding. Length Lcc is the clear length of the column C between ends of gusset plates G, and length Lbc is the clear length of the beam Bm between ends of gusset plates G.
The addition of the prior art gusset plate, which can be welded to the beam and column, creates fixity where relative motion of the beam Bm and column C is not possible. In practice, this leads to the introduction of large internal forces applied to portions of the beams and columns. FIG. 1B shows respective bending moments Mb/Mc in the beam Bm and column C and respective shear forces Vb/Vc in the beam Bm and column C that are resultant in a structure from the use of a bolted/welded gusset plate G. Also shown are the bending moment Mbr and shear force Vbr for brace Br. While FIG. 1B shows a bolted configuration between the beam Bm and column C, the same forces occur in welded joints (and welded and bolted) configurations as shown in FIG. 1C.
Shear force Vb is proportional to bending moment Mb and beam clear length Lbc (i.e., Vb∝Mb/Lbc). Likewise, shear force Vc is proportional to bending moment Mc and column clear length Lcc (i.e., Vc∝Mc/Lcc). Increasing the width and height of the gusset plates to strengthen the joints directly reduces the beam clear length Lbc and column clear length Lcc, which in turn causes larger shear forces Vb and Vc to occur for otherwise the same bending moments Mb and Mc applied to the structure by external forces (e.g., winds, earthquakes, etc.). In extreme situations these large internal forces can fracture the beam, the beam to column bolted/welded assembly, the column, and/or the gusset welds, if the prior art connection parts are not designed accordingly. However, if all the prior art connection parts are designed to accommodate the large internal forces, then structure weight, material requirements, and cost increase significantly.